829 research outputs found
Dynamic effects of electromagnetic wave on a damped two-level atom
We studied the dynamic effects of an electromagnetic(EM) wave with circular
polarization on a two-level damped atom. The results demonstrate interesting ac
Stark split of energy levels of damped atom. The split levels have different
energies and lifetimes, both of which depend on the interaction and the damping
rate of atom. When the frequency of the EM wave is tuned to satisfy the
resonance condition in the strong coupling limit, the transition probability
exhibits Rabi oscillation. Momentum transfer between atom and EM wave shows
similar properties as the transition probability under resonance condition. For
a damped atom interacting with EM field, there exists no longer stable state.
More importantly, if the angular frequency of the EM wave is tuned the same as
the atomic transition frequency and its amplitude is adjusted appropriately
according to the damping coefficients, we can prepare a particular 'Dressed
State' of the coupled system between atom and EM field and can keep the system
coherently in this 'Dressed state' for a very long time. This opens another way
to prepare coherent atomic states.Comment: latex, 2 figure
Cytological analysis of MRE11 protein during early meiotic prophase I in Arabidopsis and tomato
Early recombination nodules (ENs) are multiprotein complexes that are thought to be involved in synapsis and recombination, but little is known about their components or how they may be involved in these events. In this study, we describe the cytological behavior of a possible EN component, MRE11, a protein that is important for the repair of the numerous, programmed deoxyribonucleic acid double-strand breaks (DSBs) that occur early in the meiotic prophase. By immunofluorescence, many MRE11 foci were associated with chromosomal axes during early prophase I in both wild-type Arabidopsis and tomato primary microsporocytes. Similar patterns of MRE11 foci were observed in two Arabidopsis mutants (Atspo11-1 and Atprd1) that are defective in DSB formation and synapsis. In tomato chromosomes, MRE11 foci were more common in distal euchromatin than in proximal heterochromatin, consistent with known EN patterns. However, electron microscopic immunogold localization demonstrated that only about 10% of ENs were labeled, and most MRE11 label was associated with synaptonemal complex components. Thus, in plants, MRE11 foci are not dependent on DSB formation, and most MRE11 foci do not correspond to ENs. More generally, our results show that the simple presence of large numbers of fluorescent foci associated with synapsing chromosomes is insufficient evidence to equate these foci with ENs
Unitarity Restoration in the Presence of Closed Timelike Curves
A proposal is made for a mathematically unambiguous treatment of evolution in
the presence of closed timelike curves. In constrast to other proposals for
handling the naively nonunitary evolution that is often present in such
situations, this proposal is causal, linear in the initial density matrix and
preserves probability. It provides a physically reasonable interpretation of
invertible nonunitary evolution by redefining the final Hilbert space so that
the evolution is unitary or equivalently by removing the nonunitary part of the
evolution operator using a polar decomposition.Comment: LaTeX, 17pp, Revisions: Title change, expanded and clarified
presentation of original proposal, esp. with regard to Heisenberg picture and
remaining in original Hilbert spac
Order Parameter at the Boundary of a Trapped Bose Gas
Through a suitable expansion of the Gross-Pitaevskii equation near the
classical turning point, we obtain an explicit solution for the order parameter
at the boundary of a trapped Bose gas interacting with repulsive forces. The
kinetic energy of the system, in terms of the classical radius and of the
harmonic oscillator length , follows the law , approaching, for large , the
results obtained by solving numerically the Gross-Pitaevskii equation. The
occurrence of a Josephson-type current in the presence of a double trap
potential is finally discussed.Comment: 11 pages, REVTEX, 4 figures (uuencoded-gzipped-tar file) also
available at http://anubis.science.unitn.it/~dalfovo/papers/papers.htm
H I ABSORPTION TOWARD H II REGIONS AT SMALL GALACTIC LONGITUDES
We make a comprehensive study of H I absorption toward H II regions located within |l| < 10°. Structures in the extreme inner Galaxy are traced using the longitude-velocity space distribution of this absorption. We find significant H I absorption associated with the Near and Far 3 kpc Arms, the Connecting Arm, Bania's Clump 1, and the H I Tilted Disk. We also constrain the line-of-sight distances to H II regions, by using H I absorption spectra together with the H II region velocities measured by radio recombination lines
Damped Bloch oscillations of cold atoms in optical lattices
The paper studies Bloch oscillations of cold neutral atoms in the optical
lattice. The effect of spontaneous emission on the dynamics of the system is
analyzed both analytically and numerically. The spontaneous emission is shown
to cause (i) the decay of Bloch oscillations with the decrement given by the
rate of spontaneous emission and (ii) the diffusive spreading of the atoms with
a diffusion coefficient depending on {\em both} the rate of spontaneous
emission and the Bloch frequency.Comment: 10 pages, 8 figure
Thermalization of an impurity cloud in a Bose-Einstein condensate
We study the thermalization dynamics of an impurity cloud inside a
Bose-Einstein condensate at finite temperature, introducing a suitable
Boltzmann equation. Some values of the temperature and of the initial impurity
energy are considered. We find that, below the Landau critical velocity, the
macroscopic population of the initial impurity state reduces its depletion
rate. For sufficiently high velocities the opposite effect occurs. For
appropriate parameters the collisions cool the condensate. The maximum cooling
per impurity atom is obtained with multiple collisions.Comment: 4 pages 6 figure
Towards the noise reduction of piezoelectrical-driven synthetic jet actuators
This paper details an experimental investigation aimed at reducing the noise output of piezoelectrical-driven synthetic jet actuators without compromising peak jet velocity. Specifically, the study considers double-chamber ('back-to-back') actuators for anti-phase noise suppression and corrugated-lobed orifices as a method to enhance turbulent mixing of the jets to suppress jet noise. The study involved the design, manufacture and bench test of interchangeable actuator hardware. Hot-wire anemometry and microphone recordings were employed to acquire velocity and noise measurements respectively for each chamber configuration and orifice plate across a range of excitation frequencies and for a fixed input voltage. The data analysis indicated a 32% noise reduction (20 dBA) from operating a singlechamber, circular orifice SJA to a double-chamber, corrugated-lobed orifice SJA at the Helmholtz resonant frequency. Results also showed there was a small reduction in peak jet velocity of 7% (~3 m/s) between these two cases based on orifices of the same discharge area. Finally, the electrical-to-fluidic power conversion efficiency of the double-chamber actuator was found to be 15% across all orifice designs at the resonant frequency; approximately double the efficiency of a single-chamber actuator. This work has thus demonstrated feasible gains in noise reduction and power efficiency through synthetic jet actuator design
Stability of Repulsive Bose-Einstein Condensates in a Periodic Potential
The cubic nonlinear Schr\"odinger equation with repulsive nonlinearity and an
elliptic function potential models a quasi-one-dimensional repulsive dilute gas
Bose-Einstein condensate trapped in a standing light wave. New families of
stationary solutions are presented. Some of these solutions have neither an
analog in the linear Schr\"odinger equation nor in the integrable nonlinear
Schr\"odinger equation. Their stability is examined using analytic and
numerical methods. All trivial-phase stable solutions are deformations of the
ground state of the linear Schr\"odinger equation. Our results show that a
large number of condensed atoms is sufficient to form a stable, periodic
condensate. Physically, this implies stability of states near the Thomas-Fermi
limit.Comment: 12 pages, 17 figure
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